Tm. Vaccaro et J. Mitrofanis, RETICULAR THALAMIC REGION IN THE RABBIT - ORGANIZATION OF EFFERENTS TO THE SUPERIOR COLLICULUS, Journal of comparative neurology, 369(2), 1996, pp. 209-219
Although it is well-established that the reticular thalamic nucleus pr
ovides a strong GABAergic input to the dorsal thalamus, the existence
of reticular efferents to other subcortical centres is less certain. I
n this study, we investigate whether the reticular nucleus projects to
a major brainstem centre, the superior colliculus. The neuronal trace
r, biotinylated dextran, was injected into superficial and deep layers
of the superior colliculus of rabbits and the resultant labelling in
the reticular region was examined. After large injections, which encom
passed both superficial and deep collicular layers, two discrete popul
ations of retrogradely labelled cells are seen in the region of the re
ticular nucleus. One population of retrogradely labelled cells lies in
the dorsocaudal regions of the reticular nucleus, the classically def
ined visual sector. This group of retrogradely labelled reticular cell
s is also seen after injections into the superficial layers of the sup
erior colliculus, but not after injections limited to the deeper colli
cular layers. The other population lies close to the ventromedial edge
of the main body of the reticular nucleus, within a region referred t
o as the inner small-celled region. This group of small cells has been
commonly thought to be part of the reticular nucleus, but our immunoh
istochemical studies suggest that this is a clearly separate region, a
region continuous ventrally with zona incerta. The retrogradely label
led cells in the inner small-celled region are seen also after injecti
ons limited to the deeper collicular layers, but not after injections
limited to the superficial collicular layers. Our results suggest func
tional heterogeneity within the reticular nucleus: Specifically, it su
ggests that the nucleus is in a position to influence the processing o
f visual information at both the dorsal thalamic and midbrain levels.
(C) 1996 Wiley-Liss, Inc.